A Paradoxical Planet Beckons and Perplexes
To find a Great Lake’s worth of water frozen just beneath the arid surface of Mars may seem surprising. But Mars is a planet of contradictions, a great optical illusion that always manages to be at least two mutually exclusive things at once.
The first great contradiction, highlighted by the results now in from NASA’s Mars Odyssey mission, is between the wet and the dry. There is scarcely enough water in Mars’ thin atmosphere to fill a city’s swimming pools. And yet its surface has been scarred by floods more prodigious than any on Earth. Many of its craters seem to have been filled with lakes or seas at some time. There are features around its northern plains that some scientists interpret as the shorelines of an ocean. Where has all that water gone? The ice layer discovered in the planet’s high latitudes may be some of the answer, but it has been detected only near the surface. Can there really be an ocean’s worth beneath?
Second contradiction: the new and the old. All the ice discovered by Mars Odyssey cannot have been where it is for very long. We know that Mars wobbles on its axis and that sometimes those wobbles result in the areas where the ice now sits being warmed up and the ice released as vapor. So water does not just exist on Mars, it also circulates. Circulating water erodes things, even if it circulates only slowly and intermittently. And yet vast tracts of the Martian surface seem to have lasted without erosion for billions of years. How can Mars be active and yet so well preserved?
One thing that the ice does seem to confirm is that Mars is a place where people might live. Mars boasts sources of water (and thus of hydrogen and oxygen), carbon and nitrogen, the basic building blocks of life. It enjoys days similar in length to those of the Earth and receives enough sunlight for plants to photosynthesize. Mars is thus the only planet or moon in the solar system that one can imagine as humanity’s second home.
And yet Mars is a horrible place. Its atmosphere is as thin as our stratosphere and devoid of oxygen. Its surface is colder than Antarctica and bathed in radiation. Its soil is laced with what seems to be bleach, and its all-pervading dust may carry enough heavy metals to make the whole planet a Superfund site. Mars is the most Earth-like of the other planets and at the same time hostile and alien beyond our comprehension.
One form of earthliness, though, inspires scientists’ dreams: life. If there are to be human expeditions to Mars, the driving goal will be to look for life in places that robots can’t reach.
But the better the odds on Martian life become, the harder human exploration will be. Studying an alien ecosystem that could be very fragile, or dangerous to humans, without contamination in either direction is something that we have no idea how to do. The National Academy of Sciences has advised NASA that humans should go only to parts of Mars that have been certified thoroughly lifeless. Any landing site for humans will be meticulously scouted out by robots before a crew touches down; no one will ever climb to the top of a Martian hill without already knowing what lies on the other side.
But that does not make climbing to the top pointless. To know of somewhere and to be there are not the same. And the difference would be felt by everyone watching and sharing the astronauts’ progress across the far-off desert in the sky. The happiest contradiction Mars offers is the chance for the farthest-flung humans in history to be, for a while, at the center of our world.
